A study in conducted in China has found students lacking sleep tend to be poor performers in comparison to those who have enough sleep.
Doctors at Shanghai Children's Medical Centre studied students of 10 local primary schools. They divided the students into two groups one slept less than nine hours a day and the other group sleeping over 10 hours a day.
"The group that slept less scored lower in all the eight test categories from memory, logic reasoning to attention," said lead researcher Jiang Fan.
"The result surprised us as we never realised that the amount of sleep can make such a big difference in children," Jiang added.
Primary school students should sleep for 10 hours per day while those at middle school should sleep for nine hours, she said.
"However many children don't have enough sleep due to heavy academic burden, bad sleeping habit and parents' low awareness," she said.
"About 20 to 30 percent of children have sleep problems, which can result in higher risks of hypertension, obesity and diabetes in their adult years," Jiang said.